JPH0955179A - Beam scanning wave-form shaping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved beam scanning wave-form shaping method capable of simply and instantly judging the correctness of the generated scanning signal wave-form. SOLUTION: A detecting coil 70 detecting the time-wise change of the magnetic field of a scanning electromagnet 64 is provided. After wave-form shaping, the scanning electromagnet 64 is driven based on the scanning signal W(t) of the wave-form newly generated by the wave-form shaping, the wime-wise change of the magnetic field of the scanning electromagnet 64 is detected by the detecting coil 70, the detection signal S is compared with the preset reference data by a wave-form shaping controller 40, and the correctness of the generated wave-form is judged based on the difference between them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an ion implantation apparatus of a type in which an ion beam is electrically scanned (that is, by an electric field or a magnetic field) to implant ions into a target. The present invention relates to a beam scanning waveform shaping method capable of improving implantation uniformity by correcting a scanning speed of an ion beam.

[0002]

2. Description of the Related Art The same applicant previously proposed a beam scanning waveform shaping method capable of improving the uniformity of implantation by making the scanning speed of an ion beam on a target constant. (JP-A-4-22900
issue). The main points will be described below.

FIG. 6 is a schematic diagram showing an example in which a structure for carrying out a conventional beam scanning waveform shaping method is added to an ion implantation apparatus of a parallel scan type by an electric field.

This ion implanter electrically scans a spot-like ion beam 2 extracted from an ion source (not shown) and subjected to mass analysis, acceleration, etc., by an upstream scanning electrode 4. And is electrically bent back by the scanning electrode 6 on the downstream side, the ion beam 2 is parallel-scanned in the X-direction (for example, the horizontal direction; hereinafter the same), and the Z-direction orthogonal to the X-direction. Obtain a parallel beam parallel to the
The target (for example, wafer) 8 held at 0 is irradiated.

A scanning power supply 50 is connected to both scanning electrodes 4 and 6.
Therefore, the scanning voltages V (t) having a waveform close to a triangular wave are 1
The voltages are applied with a phase difference of 80 degrees, and the ion beam 2 is scanned with this voltage. The scanning power supply 50 is composed of an amplifier in this example, and the scanning voltage V (t) is obtained by voltage-amplifying the scanning signal W (t) output from the waveform shaping / controller 40 described later.

In this example, the holder 10 and the target 8 are mechanically scanned by a holder driving device 12 in a Y direction (for example, a vertical direction; the same applies hereinafter) substantially perpendicular to the X direction, and the holder 10 and the target 8 and the ion beam 2 are scanned. By the cooperation with the electric scanning (hybrid scanning), the ions are uniformly implanted on the entire surface of the target 8.

In this example, the holder driving device 12 is configured to reciprocally rotate an arm 13 supporting the holder 10 by a reversible motor (for example, direct drive motor) 14 within a predetermined angle range as indicated by an arrow R. ing.

First and second multipoint beam monitors 20 and 22 are arranged on the upstream side and the downstream side of the implantation position with respect to the target 8 in the beam traveling direction (Z direction), respectively. Each of the multipoint beam monitors 20 and 22 includes a plurality of Faraday cups 21 and 23 that receive the ion beam 2 and measure the beam current thereof.
Are arranged at equal intervals along the X direction, which is the scanning direction of. The position of each Faraday cup 21, 23 in the X direction is known in advance. The upstream multi-point beam monitor 20 is placed in the beam orbit when measuring the beam current, and when the ion beam 2 is passed backward to enter the target 8 or the multi-point beam monitor 22. , Out of beam orbit.

A beam current converter 30 is connected to both the multi-point beam monitors 20 and 22. The beam current converter 30 switches the amplifier 34 for amplifying the input beam current I, the A / D converter 36 for A / D conversion, and the input to the multipoint beam monitor 20 side and the multipoint beam monitor 22 side. The switch 32 is provided. The beam current converter 30 can independently measure the beam current I input to each of the plurality of Faraday cups 21 or 23 forming the multipoint beam monitor 20 or 22. The signal representing the measured beam current I is the waveform shaping / controller 4
0 is supplied.

The waveform shaping / controller 40 is a C for arithmetic processing.
It has a PU 42, a memory 44 for data storage, and a D / A converter 46 for D / A conversion. With the following logic, a scanning signal W ( generate t). The scanning voltage V (t)
Is a signal obtained by simply amplifying the scanning signal W (t), the two can be replaced in the following equation.

First, the triangular wave-shaped initial scanning signal W (t) is applied from the waveform shaping / controlling device 40 to the scanning power source 50 to scan the ion beam 2 with the initial scanning voltage V (t), and The multipoint beam monitor 20 samples the ion beam 2 being scanned. An example of the waveform of the beam current I obtained by this is shown in FIG. The horizontal axis is the time axis, and T is one reciprocating scan. The solid line in the figure is the signal from the Faraday cup 21 (for example, X = X _f1 ) of the multipoint beam monitor 20, and the broken line is the signal from the faraday cup 21 inside (for example, X = X _f2 ) thereof. The peak time indicates that the ion beam 2 is incident on the front surface of the Faraday cup 21 having the multipoint beam monitor 20 at that time. Thus, the time at which the ion beam 2 is incident on each Faraday cup 21 of the multipoint beam monitor 20 whose position {X _f1 , X _f2 , ..., X _fn } is known in advance { T _f1 , T _f2 ,
..., T _fn } is obtained.

Similarly, a multi-point beam monitor 2 on the downstream side is provided.
2, the position of each Faraday cup 23 {X
Data of the incident times {T _b1 , T _b2 , ..., T _bn } of the ion beam 2 with respect to _b1 , X _b2 , ..., X _bn } are obtained.

The scanning voltage V (and of course the scanning signal W) is
Since this is a function V (t) for time t, this function V
(T) and the previous data {T _f1 , ..., T _fn } and {T _{f1
From b1} , ..., T _bn }, two multi-point beam monitors 20
And 22 (that is, positions of Z = Z _f and Z = Z _b ), a series of data points {(V _f1 , X _f1 ), (V that indicates the relationship between the value of the scanning voltage V and the scanning position X of the ion beam 2) _f2 , X
_f2 ), ..., (V _fn , X _fn )} and {(V _b1 ,
X _b1 ), (V _b2 , X _b2 ), ..., (V _bn , X _bn )} are obtained. Simply speaking, if the time t is known, the value of the scanning voltage V at that time is known, and similarly, if the time t is known, the scanning position at that time is known.
If the value of the scanning voltage V is known, the scanning position X
Is to understand.

The multipoint beam monitor 20 (Z = Z _f ) and the multipoint beam monitor 22 (Z = Z _b ) are subjected to high-order function approximation by the least square method using this data point sequence.
The functions X _f (V) and X _b (V) representing the relationship between the scanning voltage V and the scanning position X of the ion beam 2 at are calculated. These two functions and multipoint beam monitor 20 (Z = Z _f), multipoint beam monitor 22 (Z = Z _b) and target 8 (Z =
_Zt ), a function X representing the relationship between the scanning voltage V and the scanning position X of the ion beam 2 on the target 8.
_t (V) is expressed as follows.

[0015]

[Number 1] _{X t (V) = {(} Z b -Z t) X f (V) + (Z t -
Z _f ) X _b (V)} / (Z _b −Z _f ).

Further, the scanning velocity dX _t (V) / d of the ion beam 2 at the beam scanning position X on the target 8.
t is expressed as follows.

[0017]

## EQU00002 ## dX _t (V) / dt = {dX _t (V) / dV} .multidot.
{DV (t) / dt}

Since the implantation uniformity on the target 8 is the reciprocal of the scanning speed of the ion beam 2, the predicted uniformity at the time of ion implantation at the scanning signal W (t) at that time and at the scanning voltage V (t). Is obtained by obtaining {dX _t (V) / dt} ⁻¹ in the waveform shaping / controller 40.

If the predicted uniformity is worse than that set in advance, the waveform of the scanning signal W (t) is shaped so as to satisfy the following equation, and the scanning signal W (t) having a new waveform is created.
This is performed in the waveform shaping / controller 40. C is a constant. By doing so, the scanning speed dX _t (V) / dt of the ion beam 2 on the target 8 becomes closer to a constant value, and the implantation uniformity is improved.

[0020]

## EQU3 ## W (t) / dt = C / {dX _t (V) / dV}

The above situation will be described with reference to the drawings. When the scanning voltage V is a perfect triangular wave, the function X _t (V) representing the scanning position of the ion beam of the equation 1 is normally a straight line. However, if one example is shown, it will be slightly S-shaped as shown in FIG. This is because when the trajectory of the ion beam 2 has a large amplitude as shown in FIG. 6, the ion beam 2 passes near the electrode having a high potential (positive potential) while passing through the scanning electrode 6 on the downstream side. The ion beam 2 is decelerated to increase the effect of bending back, and the ion beam 2 tends to focus slightly toward the center. Therefore, in scanning with a constant dV / dt = triangular wave, the scanning speed is small in a small amplitude portion. Is faster and the scanning speed is slower in a large amplitude portion.

The derivative of this function X _t (V) dX _t (V) /
The outline of dV is shown in FIG. This represents the scanning speed with the scanning voltage V as a variable. Therefore, if this is left as it is, the amount of ion implantation into the target 8 increases toward the periphery thereof.

In order to correct such nonuniform scanning speed, the derivative dV (t) / dt of the scanning voltage V (t).
As shown in FIG. 10, the derivative dX _t (V) /
It is sufficient to shape the scanning signal waveform and thus the scanning voltage waveform so that the derivative of the equation 2, that is, the scanning speed dX _t (V) / dt, is made constant by changing it in a relationship opposite to dV. .

The scanning voltage V (t) thus shaped
An example of the waveform of is shown by the solid line F in FIG. Broken line E in the figure
Is the original triangular wave, and in comparison, the solid line F has a sharper shape near its peak. In this example, the scanning signal W (t) that is the source of such a waveform is waveform shaped
It is generated by the controller 40, which is supplied to the scanning power source 50 to generate the scanning voltage V (t). Such a scanning voltage V
If the ion beam 2 is scanned by (t), the scanning speed of the ion beam 2 on the target 8 becomes constant even if there is unevenness in the bending back action of the ion beam 2, so that the surface of the target 8 is The uniformity of the injection amount can be improved.

[0025]

As can be seen from the above, the scanning speed of the ion beam 2 is conventionally set to the target 8
Multi-point beam monitors 20 and 2 for uniformity above
The waveform shaping process was performed using only the position data of the ion beam 2 measured by 2.

However, this method is affected by fluctuations in the ion beam 2. For example, if the barycentric position of the beam current density distribution in the ion beam 2 shifts due to a sudden change in the beam current of the ion beam 2, the position of the ion beam 2 will shift and measurement will be performed. Will be wrong.

Therefore, when performing waveform shaping by the above method, the stability of the ion beam 2 and the state of the ion beam 2 such as energy fluctuations due to discharge in the ion source and the like are monitored in detail, and at that time. There is the complexity of having to check that the sampled ion beam position data is valid.

Further, in order to check the correctness of the waveform of the scanning signal W (t) newly created by the waveform shaping process, the above-mentioned sampling of the ion beam by the multipoint beam monitors 20 and 22 is performed again. It is necessary to execute all the processes up to the calculation of the prediction uniformity, and this takes a few minutes on the order of at least, so the processing efficiency (throughput) of the target 8 is reduced accordingly.

Therefore, the present invention is improved so that the legitimacy of the created scanning signal waveform can be determined easily and instantaneously without the need to monitor the legitimacy of the sampled ion beam position data in detail. The main object of the present invention is to provide a beam scanning waveform shaping method.

[0030]

In order to achieve the above object, the beam scanning waveform shaping method of the present invention is provided with a detector for detecting a temporal change of a magnetic field or an electric field in the scanning means, and after the waveform shaping. Furthermore, the scanning means is driven on the basis of the shaped scanning signal of the waveform, the time change of the magnetic field or electric field in the scanning means at that time is detected by the detector, and the detection signal from this detector is It is characterized in that the validity of the created waveform is judged by comparing with preset reference data and the difference between the two.

According to the above method, when there is no abnormality in the generated waveform, there is little or no difference between the detection signal from the detector and the reference data given in advance.
If there is something wrong with the created waveform, the difference between this detection signal and the reference data becomes large, so the difference between the two causes
The validity of the generated waveform can be determined independently of the waveform shaping. Moreover, this determination processing can be performed easily and instantaneously because it is sufficient to compare the detection signal from the detector with the reference data.

[0032]

1 is a schematic diagram showing an example in which a configuration for carrying out a beam scanning waveform shaping method according to the present invention is added to an ion implantation apparatus of a parallel scan system by a magnetic field. The same or corresponding portions as those of the conventional example in FIG. 6 are denoted by the same reference numerals, and the differences from the conventional example will be mainly described below.

In this embodiment, the ion beam 2 is scanned by a magnetic field, more specifically, parallel scanning is performed. Therefore, the scan electrodes 4 and 6 shown in FIG.
Instead of the above, a scanning electromagnet 64 for scanning the ion beam 2 in the X direction by a magnetic field and a parallelizing electromagnet 66 for forming a parallel beam by bending the scanned ion beam 2 back by the magnetic field are provided. Scanning electromagnet 6
In FIG. 1, two upper and lower coils constituting the coil are shown as 4.

Since the scanning electromagnet 64 is used, in this embodiment, the scanning signal J (t) obtained by current-amplifying the above-mentioned scanning signal W (t) given from the waveform shaping / controller 40 in the scanning power supply 50. ) Is supplied to the scanning electromagnet 64 to drive it.

Even when the ion beam 2 is scanned by the magnetic field in this way, the method of shaping the waveform of the scanning signal W (t) and hence the scanning current J (t) is the same as in the case of the above-mentioned conventional example. The same is true, and basically, the previous scanning voltage V (t) may be replaced with the scanning current J (t).

A characteristic of this embodiment is that the scanning electromagnet 64 is provided with a detection coil 70 as a detector for detecting the temporal change of the magnetic field therein, and the detection signal S from this detection coil 70 is provided. A / D with A / D converter 72
It is adapted to be converted and taken into the waveform shaping / control device 40.

The detection coil 70 is, for example, a coil wound around the magnetic pole of the scanning electromagnet 64 for one turn, and when the magnetic flux density B in the scanning electromagnet 64 changes with time, its time change dB / dt. An electromotive force proportional to is generated, and this is output as the detection signal S.

That is, the detection signal S is proportional to dB / dt,
The magnetic flux density B is the scanning current J supplied to the scanning electromagnet 64.
Since it is proportional to (t), the detection signal S is eventually dJ (t).
Proportional to / dt. Therefore, a slight change in the inclination of the scanning current J (t) is enlarged and appears in the detection signal S.

For example, the scanning position X of the ion beam 2 is proportional to the magnetic flux density B (that is, X is represented by a linear function of B). In scanning, if the scanning speed of the ion beam 2 is constant, the value of the detection signal S should be constant.

Therefore, in this embodiment, in the waveform shaping / controller 40, first, the multi-point beam monitors 20 and 22.
The waveform of the scanning signal W (t) is shaped by the same method as described in the conventional example by using the beam current data from No. 1 to create the scanning signal W (t) having a new waveform. Thereafter, the scanning signal W (t) is further output to output the scanning power supply 50.
And the scanning current J (t) is amplified by the scanning electromagnet 6
4 is driven, the detection signal S at that time is measured, and the data is taken into the waveform shaping / controller 40.

An example of the scanning current J (t) and the detection signal S at this time is shown in FIG. A change portion P of a slight inclination of the scanning current J (t) is enlarged and appears as a large change portion Q in the detection signal S.

In the waveform shaping / controller 40, the value (for example, the absolute value) of the detection signal S when the scanning current J (t) is normal is set in advance as reference data. Then, in the waveform shaping / controlling device 40, the measured detection signal S is compared with the reference data, and the correctness of the waveform of the newly created scanning signal W (t) is determined based on the difference between the two.
Specifically, if the difference between the two is more than a certain value, it is determined that the waveform shaping has failed. The reason why waveform shaping fails is
This is because the data collected by the multipoint beam monitors 20 and 22 has some inconvenience that the scanning signal W (t) cannot be normally created.

According to the above method, the validity of the waveform of the scanning signal W (t) newly created by the waveform shaping is determined by using the detection signal S from the detection coil 70, independently of the waveform shaping. can do. Moreover, this determination process is
Since it suffices to compare the detection signal S from the detection coil 70 with the reference data, it can be performed easily and instantaneously. Therefore, unlike the conventional case, the complexity of monitoring the validity of the collected ion beam position data in detail is released. As a result, it is possible to easily realize the guarantee of the injection uniformity for the target 8 and the improvement of the reliability without much labor and time.

When the legitimacy of the shaped waveform is checked as described above and it is determined that the shaped waveform is not normal, the process proceeds further and a new scanning signal W (t) is generated in a short time as follows. It is also possible to create.

That is, the position on the detection signal S and the position on the scanning current J (t) correspond to each other as shown in FIG. 2, and the scanning current J (t) and the multi-point beam monitor 2 are also provided.
Since the scanning positions of the ion beam 2 on 0 and 22 correspond to each other as described above (see the explanation about the front part of Formula 1, but the scanning voltage V is replaced with the scanning current J), the detection signal If the position of the large fluctuation portion Q in S is known, the position on the multipoint beam monitors 20 and 22 corresponding to that portion, that is, the number Faraday cup 21.
It can be seen whether and 23 and 23 correspond to the varying portion Q. Therefore, only the data from the Faraday cups 21 and 23 corresponding to the varying portion Q are re-acquired, the data of the other portions are used as they are, and the scanning signal W (t) is re-created using these data.

According to this method, the data can be reacquired only at the inconvenient portion, so that a new scan signal W (t can be obtained in a shorter time than in the case where the scan signal W (t) is created with all new data. There is an advantage that t) can be created.

By the way, first, the scanning electromagnet 64 having the characteristic that the scanning position X of the ion beam 2 is proportional to the magnetic flux density B is obtained.
Is normal, but it may be not so, so that case will be described.

For example, as in the example shown in FIG. 3, X∝√B
When the ion beam 2 is scanned by the scanning electromagnet 64 having the above characteristic, in order to scan the ion beam 2 at a constant speed, the scanning current J supplied to the scanning electromagnet 64 is supplied.
The waveform of (t) is not a perfect triangular wave as shown in FIG. 2, but X ² or t near the upper and lower sides of the triangular wave as shown in FIG.
^It is necessary to form a waveform that is bent in proportion to ² .

When the scanning electromagnet 64 is driven by such a scanning current J (t), the waveform of the detection signal S output from the detection coil 70 is approximately as shown in FIG.
This is the normal waveform. Therefore, this waveform is stored in the waveform shaping / controller 40 in advance as reference data.

Then, when determining the correctness of the shaped waveform, the waveform of the detection signal S measured at that time is compared with the reference data waveform, and the correctness of the shaped waveform is determined based on the difference between the two.

In the above, the case of the so-called parallel scan system in which the ion beam 2 scanned by the scanning electromagnet 64 or the scanning electrode 4 is bent back by the collimating electromagnet 66 or the scanning electrode 6 to form a parallel beam has been described as an example. However, as can be seen from the above description, the target of waveform shaping is basically the scanning electromagnet 64.
Alternatively, it has a waveform of the scanning current J (t) or the scanning voltage V (t) to be supplied to the scanning electrode 4, and a parallelizing electromagnet 66 or a scanning electrode 6 is further provided on the downstream side thereof to convert the ion beam 2 into a parallel beam. Whether or not this does not affect the essence of the present invention is arbitrary.

Further, as shown in FIG. 6, in the case of the system in which the ion beam 2 is scanned by the electric field in the scanning electrode 4, as a detector for detecting the temporal change of the electric field in the scanning electrode 4, for example, FIG. It is sufficient to provide a set of detection probe 74 and differentiator 76 as shown in FIG. The detection probe 74 is inserted between the two scanning electrodes 4 to detect the electric field E at the scanning electrodes 4 and differentiated by the differentiator 76 to obtain a time change dE of the electric field E at the scanning electrodes 4. A detection signal S representing / dt can be obtained. The reason why the differential is obtained is that, as in the case of the example of FIG. 1, a minute change in the inclination of the electric field E is enlarged and appears in the detection signal S, and the change can be easily detected.

Since the method of determining the correctness of the shaped waveform using the detection signal S is the same as that shown in FIG. 1, the duplicated description will be omitted here.

As the detector, the detection coil 7 shown in FIG.
Comparing the case where 0 is used and the case where the combination of the detection probe 74 and the differentiator 76 shown in FIG. 5 is used, the detection coil 70 is less affected by noise and the differentiator is not necessary. , Easy and accurate.

[0055]

As described above, according to the present invention, the legitimacy of the created scanning signal waveform can be judged independently of the waveform shaping by using the detection signal from the detector. Moreover, this determination processing can be performed easily and instantaneously because it is sufficient to compare the detection signal from the detector with the reference data. Therefore, unlike the conventional case, the complexity of monitoring the validity of the collected ion beam position data in detail is released. As a result, it is possible to easily realize the guarantee of the implantation uniformity for the target and the improvement of the reliability without much labor and time.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example in which a configuration for implementing a beam scanning waveform shaping method according to the present invention is added to a parallel scan type ion implantation apparatus using a magnetic field.

FIG. 2 is a diagram showing an example of waveforms of a scanning current and a detection signal in FIG.

FIG. 3 is a diagram showing an example in which a beam scanning position is not represented by a linear function of magnetic flux density.

FIG. 4 is a diagram showing an example of waveforms of a scanning current and a detection signal in the case of a scanning electromagnet having the characteristics of FIG.

FIG. 5 is a diagram showing an example of a detector used when an ion beam is scanned by an electric field.

FIG. 6 is a schematic diagram showing an example in which a configuration for carrying out a conventional beam scanning waveform shaping method is added to an ion implantation apparatus of a parallel scan system using an electric field.

FIG. 7 is a schematic diagram partially showing an example of signals from a multipoint beam monitor.

FIG. 8 is a diagram showing an example of a function representing a scanning position of an ion beam.

FIG. 9 is a diagram showing an example of a derivative of a function representing a scanning position of an ion beam.

FIG. 10 is a diagram showing an example of a derivative of a function representing a scan voltage.

FIG. 11 is a diagram showing an example of a shaped scanning voltage waveform.

[Explanation of symbols]

 2 Ion beam 8 Target 20, 22 Multi-point beam monitor 30 Beam current converter 40 Waveform shaper / controller 50 Scanning power supply 64 Scanning electromagnet 70 Detection coil

Claims (2)

[Claims] 1. A scanning current or a scanning voltage is generated based on an initial scanning signal and is used to scan an ion beam by a magnetic field or an electric field in a scanning means, and the ion beam thus scanned is electrically scanned. To determine the temporal change of the scanning position for each of the upstream side and the downstream side of the ion beam, and based on the results, the target is determined from the positional relationship between the measurement position on the upstream side and the downstream side of the ion beam and the target. The temporal change of the scanning position of the ion beam on the target is obtained, and the waveform of the scanning signal is shaped so that the temporal change of the scanning position of the ion beam on the target becomes constant. In a beam scanning waveform shaping method for creating a scanning signal, a detector for detecting a temporal change of a magnetic field or an electric field in the scanning means is provided. After the waveform shaping, the scanning means is driven based on the scanning signal of the waveform newly created by the waveform shaping, and the temporal change of the magnetic field or electric field in the scanning means at that time is detected by the detector. Then, the beam scanning waveform shaping method is characterized in that the detection signal from this detector is compared with preset reference data, and the validity of the generated waveform is judged based on the difference between the two. 2. The beam according to claim 1, wherein the scanning means is a scanning electromagnet that scans an ion beam with a magnetic field, and the detector is a detection coil that detects a temporal change in the magnetic field of the scanning electromagnet. Scan waveform shaping method.